1. Field of the Invention
The present invention relates to a pressure-regulating device for supplying a gas to a container, comprising an inlet intended to be connected to a source of the said gas under pressure, an outlet, connected by a duct to the said inlet and intended to be placed in communication with the container, a first valve for limiting the pressure at the said outlet to a predetermined maximum value Ps, which valve is a delivery valve placed in a first passage which connects the said duct to an orifice for discharging inert gas.
The invention applies in particular to the supply of working liquids in the electronics industry.
2. Description of the Related Art
The electronics industry, particularly the microelectronics industry, involves the use of ultrapure working liquids such as H2O2, HCl, H2S, etc., for example.
Such liquids are generally held in storage containers, the structure of which makes it possible to prevent these liquids from becoming contaminated, especially through the presence of particularly expensive and delicate internal coatings, for example perfluoroalkoxy coatings (PFA).
The delicate nature of these internal coatings considerably limits, inside these containers, the permissible variations in pressure about atmospheric pressure to which these containers are subjected externally.
Thus, the gauge pressure inside these containers must, for example, be between xe2x88x9220 and +150 mbars.
In order to observe this constraint and avoid the contamination of the working liquids that are to be dispensed, the vacuum created in such a container when working liquid is drawn off is filled by the supply of corresponding amounts of an ultrapure inert gas, typically nitrogen.
Nitrogen is generally supplied to a container for the storage of working liquid by a supply system which comprises a pressure-regulating device, means of connecting an inlet of the device to a source of inert gas under pressure, these means being equipped with means of expanding the gas to a datum pressure Pc that lies in the range of pressures which are permissible inside the container, and a pipe for placing an outlet of the device in communication with the storage container. The pressure-regulating device is intended to prevent damage to the storage container in the event of an operating incident.
Until now, there have been two types of pressure-regulating device.
In the first type, the device comprises a permanent communication with the ambient atmosphere of the duct connecting the inlet and the outlet of the regulating device, through a calibrated vent. Although this type of device provides the storage containers with good protection against variations in internal gauge pressure, it does, however, entail constant consumption of ultrapure nitrogen, whether or not working liquid is being dispensed, and this leads to high running costs.
In the second type, the pressure-regulating device comprises a delivery valve with a valve element balanced by a spring, to place the duct of the regulating device in communication with the ambient atmosphere. A device of this kind exhibits numerous drawbacks. Specifically, it does not safeguard the containers, on the one hand, against any depression and, on the other hand, in case of substantial overpressure upstream of the regulating device, because of the low delivery rates allowed by these clack-type valves. Furthermore, this type of device entails regular checks on the settings of the clack valve and of the expansion means, which are dependent on one another. Finally, as the use of metal components in such regulating devices is forbidden in order to maintain the purity of the inert gases, this type of device is complex and expensive to produce.
The object of the invention is to solve these problems by providing a simple pressure-regulating device of low manufacturing and running costs and which is able to safeguard storage containers when dispensing ultrapure working liquids.
To this end, the subject of the invention is a pressure-regulating device for supplying a gas to a container, comprising an inlet intended to be connected to a source of the said gas under pressure, an outlet, connected by a duct to the said inlet and intended to be placed in communication with the container, a first valve for limiting the pressure at the said outlet to a predetermined maximum value Ps, which valve is a delivery valve placed in a first passage which connects the said duct to an orifice for discharging inert gas, characterized in that the device also comprises a second valve for keeping the pressure at the said outlet above a predetermined minimum value Pi, which valve is an intake valve placed in a second passage which connects the said duct to an orifice that lets fluid into this duct.
According to particular embodiments, the device may have one or more of the following features, taken in isolation or in any technically feasible combination:
the first valve comprises a first shutter which can move between a lower shut-off position and an upper flow, position, under the action of a positive difference P+between the pressures in part of the duct and at the said discharge orifice, acting against the action of the self weight of the first shutter, the said shutter being of a mass carefully determined to balance the action of a predetermined pressure difference P+c;
the first shutter is placed on a seat intended to be substantially horizontal;
the discharge orifice is an orifice for communicating with the ambient atmosphere at pressure Pa, and P+c=Psxe2x88x92Pa;
the second valve comprises a second shutter which can move between a lower shut-off position and an upper flow position under the action of a negative difference Pxe2x88x92between the pressures in part of the duct and at the intake orifice, acting against the action of the self weight of the second shutter, the shutter being of a mass carefully determined to balance the action of a predetermined negative pressure difference Pxe2x88x92c;
the second shutter is placed on a seat intended to be substantially horizontal;
the intake orifice is an orifice for communicating with the ambient atmosphere at pressure Pa, and Pxe2x88x92c=Pixe2x88x92Pa.
Another subject of the invention is a system for supplying inert gas to a container, comprising a pressure-regulating device, means of connecting an inlet of the device to a source of the gas under pressure, and a pipe for placing an outlet of the device in communication with the container, characterized in that the pressure-regulating device is a device as defined hereinabove.
In an alternative form, the connecting means comprise means of expanding the inert gas to a datum pressure Pc which lies approximately between Pi and Ps, and preferably close to Ps.
A final subject of the invention is an installation for dispensing a working liquid, comprising a container for storing the working liquid, means of dispensing the working liquid which are connected to the container, a system for supplying gas, especially inert gas, to the container (4), and a source of the gas under pressure, the supply system being connected to the source and to the container so as to fill in the latter a vacuum produced as a result of the withdrawing of the liquid, characterized in that the gas-supply system is a system as defined hereinabove.